Prince Andrew has “completely shut the door” on cooperating with US investigators in the Jeffrey Epstein case and they are now “considering” further options, a New York prosecutor said on Monday.

Andrew was a friend of Epstein, the wealthy financier and convicted sex offender whose death in custody while awaiting trial on sex trafficking charges in New York last year was ruled a suicide.

Andrew denies all claims of sexual misconduct relating to the Epstein case but has stepped back from public duties as a result of his connection to it.

Speaking to reporters on Monday, the Manhattan US attorney Geoffrey Berman said: “Contrary to Prince Andrew’s very public offer to cooperate with our investigation into Epstein’s co-conspirators, an offer that was conveyed via press release, Prince Andrew has now completely shut the door on voluntary cooperation and our office is considering its options.”

In November, Andrew said he was “willing to help any appropriate law enforcement agency with their investigations if required”.

Berman made a similar claim in January, which former sex crimes prosecutors told the Guardian was most likely a move designed to win political support for the investigation.

Buckingham Palace said then it would not comment and the matter was being dealt with by the prince’s legal team. Contacted on Monday, a Palace spokeswoman said: “The issue is being dealt with by the Duke of York’s legal team.”

Buckingham Palace has consistently refused to reveal any details of Andrew’s legal team but the Duke has reportedly hired Clare Montgomery, a senior barrister at Matrix Chambers, whose clients have included Augusto Pinochet, Chile’s former dictator, and Shrien Dewani, charged with and acquitted of murdering his wife in South Africa. She also prosecuted the Metropolitan police over the death of Jean Charles de Menezes, shot dead in a failed anti-terror operation.

Andrew has been accused of having sex with a young woman provided by Epstein, a claim he categorically denies.

In a December interview with the BBC, the accuser, Virginia Giuffre, now 35, called Andrew’s denial “BS”.

“He knows what happened,” she said. “I know what happened, and there’s only one of us telling the truth, and I know that’s me.”

The Guardian has reported that according to flight logs, Andrew was among nine people on Epstein’s plane for a trip from the US Virgin Islands to Florida in February 1999.

A lawsuit filed by the US territory’s attorney general in January cites new evidence that Epstein “held captive underage girls” there as recently as 2018.

Montgomery declined to comment to an inquiry from the Guardian. She is reportedly briefed by Gary Bloxsome, a criminal defence solicitor who has defended British troops against war crime allegations. It has been reported he was appointed directly by Andrew, though this has not been confirmed by the palace.